The electric field therapy apparatus which serves to treat the human body in electric field and which is called electric potential, electrostatic, or ion therapy apparatus has been widely used as one means to attain physio-therapy and excellent therapeutical effects have been demonstrated. The feature of this electric field therapy apparatus exists in that therapeutical treatment can be easily effected all over the human body without current being applied directly to the human body.
FIG. 1 is a circuit diagram showing an example of the conventional electric field therapy apparatus. In FIG. 1, numeral 1 represents a boosting transformer, which is provided with a primary winding 2 and a secondary winding 3 which generates boosted voltage. Numerals 4, 4 denote power source terminals of a commerical power source E, 5,6 connecting points of the secondary winding 3, 7, 8 high impedance elements connected to the connecting points 5 and 6, respectively, and comprising resistors or capacitors, numerals 9, 10 connecting points, and numerals 11, 12 therapeutical electrodes, one 12 of which is connected to the earth 13 through the high impedance elements 8.
14 denote an earth connected to one line of the commercial power souce E. V.sub.1 represents a voltage applied between the power source terminals 4 and 4 of the primary winding 2, and V.sub.2 a voltage output between the connecting points 9 and 10.
In the case of the conventional electric field therapy apparatus arranged as described above, the side of the connecting point 6 of the secondary winding 3 is earthed, thereby enabling the electrode 12 to be of low withstand voltage to ground (dielectric strength against the voltage to ground, hereinafter referred to as "withstand voltage to ground") structure, but the side of the connecting point 5 of the secondary winding 3 is by about the voltage V.sub.2 higher than the side of the connecting point 6 and this voltage V.sub.2 is usually high, amounting to several kilo-volts, thereby causing the electrode 11 to be of high witstand voltage to ground structure.
When safety is considered, only the high impedance element 7 is sufficient, and the conventional apparatus is usually provided with only this high impedance element 7. When therapeutical effects attained by the electric field therapy apparatus are considered, the high impedance elements 7 and 8 are not necessarily needed.